1. Field of the Invention
The present invention relates to electronic equipment such as an electronic desk-top calculator with a unit conversion function for converting length, weight, or the like between different unit systems and to a desk-top function calculator capable of calculating a trigonometric function and others. More particularly the invention relates to an improvement in a so-called second function key system electronic equipment in which each key is provided with a plurality of arithmetic functions in addition to its primary function and a desired one of the plurality of arithmetic functions is designated by a designation key such as a conversion designation key or a function designation key.
2. Description of the Prior Art
FIG. 1 shows an example of a conventional electronic equipment, that is, a conventional unit conversion desk-top calculator with a second function key system having a unit conversion function for converting units between the English system and the metric system. Numeral 1 denotes a desk-top calculator body having a keyboard 2, including a group of numeric keys 21, and a display 3. On the keyboard 2, two unit indications between which conversion is to be made are marked, by printing or the like with arrows of opposite directions inserted therebetween, above each of the numeric keys 1 - 9 which have a second function. Numerals 4 and 5 denote unit conversion designation keys. By depressing one key 4 or 5, the desk-top calculator 1 is set to a mode (the second function mode) to carry out the unit conversion operation assigned to the depressed one of the numeric keys 1 - 9 . When the unit conversion designation key 4 is depressed, the unit conversion operation from the lefthand unit to the righthand unit indicated above the corresponding numeric keys 1 - 9 is enabled, and when the unit conversion key 5 is depressed, the reverse conversion operation, that is, from the righthand unit to the lefthand unit is enabled.
When units of numerals displayed on the display 3 are to be converted, one unit conversion designation key 4 or 5 is first depressed. Thus, the mode of the desk-top calculator 1 is switched from a normal calculation mode in which numerals are entered by the depression of the numeric keys 1 - 9 to the second function mode in which the unit conversion functions assigned to the respective numeric keys 1 - 9 are carried out. Subsequently, when one of the numeric keys 1 - 9 to which a desired unit conversion function is assigned is depressed, the unit conversion operation of the numerals displayed on the display 3 is carried out and a converted result is then displayed on the display 3.
However, in the prior art second function key system desk-top calculator of the type described above, the indication of the numeric information displayed on the display 3 is the same whether the desk-top calculator is in the normal calculation mode or in the second function mode in which the unit conversion operation is carried out. Accordingly, it is not possible to rapidly determine the mode in which the desk-top calculator is set. Further, in the second function mode, since the display of numeric information by the display 3 before the unit conversion is same as that of the numeric information displayed after the unit conversion, it is not possible to determine whether the numerals so displayed are the unconverted ones or the converted ones. This is inconvenient particularly when operation of the calculator is interrupted. Furthermore, if an operator improperly operates the unit conversion designation key, for example, if the operator depresses the key 8 instead of the key 7 to convert the inch unit (in) to the centimeter unit (cm), the conversion operation from the feed unit (ft) to the meter unit (m) is carried out. Since the operator cannot know what unit conversion operation has been carried out from the resulting numeric information displayed on the display 3, the operator may not notice that an improper operation has been carried out and may use the erroneous numeric information.